interplanetary, rather than interstellar, dust in the prominent S-shaped blue regions well above and below the galactic plane (this dust may be a remnant of asteroid collisions); and hot particles known as polycyclic aromatic hydrocarbons (PAH). PAHs are groups of 20 to 100 carbon atoms joined with hydrogen at temperatures up to 1,000 degrees Kelvin.
Infrared radiation is concentrated in the galactic plane of our galaxy. Away from the plane there are bright patches and long filaments, which scientists believe are from dust associated with HI gas in interstellar space. The patches and filaments can be quite large and are sometimes known as infrared cirrus clouds, after the high, wispy clouds in the EarthΓÇÖs atmosphere.
